Sergey G. Moiseev

Optical properties of nanostructured layers on the surface of an underlying medium

An analytical approach to the description of the optical characteristics of layers consisting of interacting nanoclusters is developed based on the integral equation method. Expressions for the fields inside and outside the system are obtained, the effective parameters of the structure elements are studied taking into account the mutual polarizing effect of nanoclusters and underlying medium, and the applicability conditions of the model proposed are determined. The possibility of controllable the tuning of the spectral properties of the system by changing its structural parameters is considered; it is shown that the reflection from the substrate surface can be decreased by depositing a nanostructured coating. Good agreement is obtained between the analytical calculation and the exact numerical solution of Maxwell’s equations.

Induced modulation instability of surface plasmon polaritons

We demonstrate the effect of the modulation instability of surface plasmon polariton waves in a layer structure of subwavelength thickness. The expressions describing the dispersion and nonlinear properties of this structure are derived. It is shown that the modulation instability effect could be used for the generation of ultrashort pulse trains and the localization of optical fields with a scale less than 1 micron.

Nanocomposite-based ultrathin polarization beamsplitter

In terms of the effective medium approximation, the optical properties of heterogeneous composite materials with disordered nanosized metal inclusions of spheroidal shape with plasmon resonances lying in the visible spectral range are studied. The conditions are analyzed under which the optical characteristics of the composite with axial symmetry of the inclusion orientation distribution with respect to a certain preferential direction significantly depends on the electric field direction in the electromagnetic wave. It is shown that, in the vicinity of the plasmon resonance of inclusions, the composite layer of subwavelength thickness may exhibit a high polarization selectivity in both reflection and transmission with moderate absorption. The effect of the orientational disorder of inclusions on the optical characteristics of a polarization splitter of this kind is discussed. The predictions based on equations of quasi-electrostatic effective-medium model agree well with the results of exact numerical solution of the Maxwell equations.

Design of antireflection composite coating based on metal nanoparticles

A design of ultrathin composite layer with metal nanoparticles on a dielectric surface is proposed for interference reduction of Fresnel reflection. The structural and material parameters of the antireflection composite are calculated within the Maxwell-Garnett effective-medium approximation. The results of the approximate analytical calculation are in good agreement with the exact numerical solution to the Maxwell equations.

Influence of size effects on the optical characteristics of a one-dimensional photonic crystal with a nanocomposite defect

The spectral characteristics of a one-dimensional photonic crystal with an inset made of a heterogeneous composite material containing metal nanoparticles of different sizes have been studied. The influence of the size-dependent relative permittivity of nanoparticles on the spectrum of the photonic crystal has been demonstrated.

Polarization fields in the positronium atom undergoing emission or absorption of optical photons

This paper solves the problem of the interaction of an electron and positron via the field of soft and hard photons with emission or absorption of a real photon. The interaction is interpreted as a third-order QED effect in the coordinate representation. The role of intermediate states with positive and negative frequencies is studied. A general expression is derived for the matrix elements of the operator of the effective electron-positron interaction energy for different types of quantum transitions. The expression makes it possible to calculate the probabilities of the corresponding transitions in the nonrelativistic approximation. Electric dipole transitions in the positronium atom accompanied by emission (absorption) of an optical photon are investigated. Two-particle wave functions of the positronium atom are used to introduce the concept of polarization fields inside the positronium atom. It is found that the polarization fields depend on the coordinates and time and on the choice of the pair of states between which a quantum transition with emission or absorption of a photon takes place.

Surface plasmon polariton amplification in a single-walled carbon nanotube

The interaction of a surface plasmon polariton wave of the far-infrared regime propagating in a single-walled carbon nanotube with a drift current is theoretically investigated. It is shown that under the synchronism condition a surface plasmon polariton amplification mechanism is implemented due to the transfer of electromagnetic energy from a drift current wave into a terahertz surface wave propagating along the surface of a single-walled carbon nanotube. Numerical calculations show that for a typical carbon nanotube surface plasmon polariton amplification coefficient reaches huge values of the order of 106 сm-1, which makes it possible to create a carbon-nanotube-based spaser.

Defect modes of one-dimensional photonic-crystal structure with a resonance nanocomposite layer

We have studied the defect modes of a structure of Fabry – Perot interferometer type, in which the layer separating Bragg mirrors is made of a heterogeneous composite material with metallic nanoscale inclusions. Effective optical characteristics of the nanocomposite material have resonance singularities in the visible region of the spectrum, which are conditioned by the surface plasmon resonance of metallic nanoparticles. It is shown that the spectral profile of the energy bandgap of the photonic structure can be modified by varying the volume fraction and size of nanoparticles. The interrelation of splitting and shift of defect modes with structural parameters of a nanocomposite layer is studied by means of a numerical – graphical method with allowance for the frequency dependences of phases and amplitudes of reflectances in Bragg mirrors.

The magnetostatic field in a terahertz rod/film structure

The magnetostatic field distribution in a structure formed from a ferromagnetic (FM) rod and thin FM film is numerically calculated. The effective terahertz radiation was previously discovered in such a structure in the presence of a current. It is shown that nanodimensional sections of the boundary between the lateral surface of the rod and the surface of the film can be a source of radiation. On these sections, the magnetostatic field changes its direction, a circumstance that provides for conditions for radiative transitions of electrons.

Optical Properties and Some Applications of Plasmonic Heterogeneous Materials

Metamaterials with extraordinary optical properties can find a variety of applications, in particular for manufacturing superlenses, prisms, nonreflecting (absorptive) materials, as well as controlling the optical beam intensity and propagation direction, etc. (Cai & Shalaev, 2010; Hutter & Fendler, 2004). In recent years, a large number of structures have been proposed and theoretically and experimentally investigated, which possess negative, high or small refractive indices (Moiseev et al., 2007; Oraevskii & Protsenko, 2000; Shalaev et al., 2005; Shen et al., 2005; Sukhov, 2005; Yuan et al., 2007), selective absorption of or transparency to optical light (Kachan et al., 2006; Kravets et al., 2008; Protsenko et al., 2007). The promising candidates for a design of structures with extraordinary optical properties are plasmonic materials. Collective electronic excitations called plasmons lead to strong dispersion and absorption of light in such artificial media. For practical applications, it is important that the optical properties of composite medium incorporating metallic nanoparticles can be controlled by careful selection of geometric parameters of nanoparticles (Moiseev, 2004, 2009; Oraevskii & Protsenko, 2000). By selecting distributions of the form of metallic nanoparticles, it is possible to achieve absorption of electromagnetic radiation in specified spectral regions of visible or near IR radiation (Protsenko et al., 2007). An additional effective way of the plasmon resonance control is by spatial arrangement of metal-dielectric nanocomposites, for example, forming the multilayer systems consisting of metallic nanoparticles separated by dielectric layers (Kachan et al., 2006). It was proposed that such composite materials with controlled absorption of light can be used as cut-of filters and high-absorbing coatings. In this work, a more detailed investigation of optical properties of a matrix metal-dielectric medium with spheroidal silver inclusions is performed, and the possibility to realize plasmonic structures with beneficial effects in the visible region is considered. In so doing, it is assumed that the characteristic size of inclusions and their volume concentration satisfy the conditions of applicability of the effective medium Maxwell–Garnett model.